README: update development setup command (#77)

Modifications:

* `README`: update `docker-compose` command for local testing
* update Docker documentation in `docker-compose.yaml`

Author: felixschlegel

README.md

@@ -151,5 +151,5 @@ It has source files that are excluded in `Package.swift`.
 We provide a Docker environment for this package. This will automatically start a local Kafka server and run the package tests.
 
 ```bash
-docker-compose -f docker/docker-compose.yaml run swift-kafka-gsoc
+docker-compose -f docker/docker-compose.yaml run test
 ```

docker/docker-compose.yaml

@@ -1,4 +1,6 @@
-# Usage: docker-compose -f docker/docker-compose.yaml run swift-kafka-gsoc
+# this file is not designed to be run directly
+# instead, use the docker-compose.<os>.<swift> files
+# eg docker-compose -f docker/docker-compose.yaml -f docker/docker-compose.2204.57.yaml run test
 version: "3.9"
 services:
 
@@ -21,9 +23,6 @@ services:
     environment:
       KAFKA_HOST: kafka
 
-  # Swift on Server CI
-  # e.g. docker-compose -f docker/docker-compose.yaml -f docker/docker-compose.2204.57.yaml run test
-
   runtime-setup:
     image: swift-kafka-gsoc:default
     build: